Recording unit for audio teaching equipment



Feb. 28, 196'? A. F. ERFF RECORDING UNIT FOR AUDIO TEACHING EQUIPMENT Filed Jan. 9,

INVENTQR F Y?? HGENT United States Patent Gti ice 3,306,988 Patented Feb. 28, 1967 3,306,988 RECORDING UNT? FOR AUDllO TEACHING EQUPMENT Anthony F. Erft, Guilford, Conn., assigner to J-B-T Instruments, Inc., New Haven, Conn., a corporation of Connecticut Filed Jan. 9, 1963, Ser. No. 250,419 7 Claims. (Cl. 179-1002) This invention relates to audio teaching equipment, and more particularly to recording units of such equipment, which are to be used at student stations.

An object of the invention is to provide a novel and improved electronic recording unit for the general purpose specified, which unit may from a remote point and in a simple manner be readily switched or controlled for the purpose of either making it operative to record signals or else making it inoperative for this purpose.

Another object of the invention is to provide an improved recorder unit as above, wherein there is both the remote control and also a proximal energizing or onoil control so arranged that both are in the nature of master switches as regards effecting the inoperative condition of the recorder, since either may dominate the other for this purpose; further,both controls are so arranged that they must be set in their operative positions for the recorder to lbe conditioned for recording purposes.

A further object of the invention is to provide an improved recording unit in accordance with the foregoing, wherein the switching or control circuit and means while being advantageously extremely simple, are yet effective and reliable in operation.

An additiond object of the invention is to -provide a novel recording unit as above set forth, wherein rst and second oscillators and also a signal amplifier are correlated by simple switch means to enable a selective control as above set forth to be readily had, and to enable selective energization of the electronic units in the most advantageous manner to be eected.

Yet another object of the invention is to provide an improved recorder of the kind described, wherein but a single additional wire is required in the control or signal cable to enable the desired remote switching to be eifected.

A feature of the invention resides in the provision of an improved recorder unit as outlined, wherein the single control wire is at low potential with respect to the ground, thereby eliminating problems of insulation, isolation and the like.

Another feature of the invention resides in the provision of a novel recorder unit having the above functions, wherein relatively few components are required, and wherein the circuits are simple, including the energizing and load circuitry.

Further features include the switching of low potentials and ows to increase useful contact life, and the use of an already existing ground return as part of lthe additional switch circuit.

' Other features and advantages will hereinafter appear.

In the drawings, the single tigure comprises a schematic circuit diagram of the student station recording unit as provided by the invention.

Considering specifically the circuit diagram given herein, the recorder unit is shown as comprising three electronic valve or relay devices 1t), 12 and 14, said devices being indicated as vacuum tubes of the triode type. The triodes 10 and 12 may constitute two sections of a 12AT7 dual triode, and the triode 14 may constitute one section of a 12AX7 dual triode. The three triodes 10, 12 and 14 are preferably mounted on a single chassis along with other components to be described, and the recording unit comprising the chassis, cabinet, etc. is indicated diagrammatically by the broken rectangular outline 16.

Leading to the recorder is a multi-wire signal and control cable 18, which goes to a remote point indicated as 20, where the main console or teaching unit rnay be located. The cable 18 has at least the two wires 18a and 181:.

The triodes 1t), 12 and 14 are shown as having, respectively, heaters 22, 24 and 26; cathodes 28, 30 and 32; control grids 34, 36 and 38; and plates or anodes 40, 42 and 44.

The triode 12 is a continually operating master oscillator. Its control grid 36 is grounded at 46. The cathode 3% connects to a cathode resistor 48 which is grounded at 5G. A bypass capacitor shunts the cathode resistor 48. The anode 42 is connected by a wire 54 to a tank inductor 56, to which a B-lvoltage is applied in a manner hereinafter explained. The B- voltage is applied to a ground terminal 58. A bypass capacitor 60 is connected between the wire S4 and the cathode 30, and an output circuit or wire 62 leads from the wire 54 to a coupling capacitor 64 which is in turn connected to a cable 66 leading to the erase head of a tape recorder unit (not shown). The coupling capacitor `64 is also shown as connected by a wire 68 to a second coupling capacitor 70 which is joined to a cable 72 leading to a recording head (not shown) associated with the aforesaid erase head. The erasing and recording heads to which the cables 66 and 72 are connected may be associated with track B of the tape recorder, for example.

In order for the student to record, utilizing the master oscillator 12 and track B of the tape recorder, a student microphone 74 is connected to have one terminal grounded at 76 and the other terminal joined to a wire 78 which is in turn connected to a coupling capacitor `8i) joined by'a wire 82 to the capacitor 70. With the master oscillator 12 thus `being continuously in operative condition, the student may record at any desired time on track B of the tape recorder.

B+ energization for the master oscillator 12 is applied to the inductor or tank coil 56 through a wire 84 connected to one terminal 86 of an onct switch S8 having a contact blade 90 connected to the B-I- terminal 92 of the unit. The plate voltage for the recorder is supplied from a convenional plate supply unit (not shown) which may be located in the same cabinet as the recorder or else at a remote point.

ln the appended claims, the master oscillator 12 is referred to as a second oscillator. The frequency of such oscillator may be on the order of 60 kilocycles for purposes of erasing and recording, such frequency being not critical, and determined by the circuit constants as will be understood.

In accordance with the present invention, in conjunction with the master oscillator 12 there is provided an additional oscillator which may receive drive from the master oscillator, and also an input amplier, these comprising respectiveiy the triodes 16 and 14, together with a novel remote control organization by which the additional oscillator and the input amplifier may be selectively rendered operative or inoperative at a remote point, as for example the location 2i), and may be switched on and off at the student position (at the unit itself). Further, the circuitry by which this is accomplished is extremely simple, is reliable in operation and characterized by a low operating potential whereby there are eliminated the problems of insulation, isolation, hazard of shock, etc.

The input amplifier 14 and the driven oscillator 1i) are associated with a second track, as for example track wires 18a and 18b which form part of the A, of the tape recorder unit (not shown) above referred to. At the recorder unit 16 the selective switching or control is correlated with the on-off swich 88 above mentioned, whereby such switch has an additional or second on position, besides the regular on position. For this additional on position of the switch 88 the input amplifier 14 and the additional oscillator 10 will be conditioned or connected for B-lenergization whereby they are ready for control from the remote point 20.

In accomplishing this, a second switch unit 96 is provided, having a contact blade 98 connected by a jumper 100 to the contact blade 90. Also, the contact blades 90, 98 are mechanically coupled to each other for simultaneous operation. The additional switch 96 has a stationary contact 102 which is engaged by the blade 98 when the blade 90 is in the additional on position engaging a lfurther stationary contact 104. The contact 104 is connected by a jumper 106 to the contact 86, as shown.

Br-lvoltage is therefore supplied to the oscillator and amplifier 14 in the following manner: The stationary contact 102 is connected by a wire 108 to a tank or inductor coil 110 which in turn is connected by a wire 112 to the anode 40 of the oscillator 10. Similarly, the switch contact 102 is connected by a wire 114 to a plate resistor 116 which is connected by a wire 118 to the anode 44 of the amplifier 14. These constitute the energizing circuits for the oscillator 10 and amplifier 14, just as the B+ circuit 54, 56 constitutes the energizing circuit for the master oscillator 12. The switches 96 and 88 are respectively in series in the energizing circuits 108, 114 and 54 of the devices 10, 14 and 12.

It will be seen that by the above switching arrangement, all three triodes 10, 12 and 14 may be energized with B+ voltage when the switches 88, 96 are in the position indicated. However, when the switch blade 90 is in engagement with the switch contact 86, only the master oscillator triode 12 will receive B-lenergization. Also, when the switch blade 90 is out of engagement with either of the stationary contacts 86 or 104, as when it is in a center position, no B-lenergization will be supplied to any of the triodes. The student may thus selectively energize either the master oscillator 12 alone, or else such oscillator in conjunction with the additional oscillator 10 and the input amplifier 14.

The oscillator 10 has an output circuit comprising a wire 122 connected with the anode 40 and with a cou- -pling capacitor 124 which latter is in turn joined by a wire 126 to a cable 128 leading to the erasing head for track A of the tape recorder unit. A wire 130 is connected with the wire 126 and also with a coupling capacitor 132, the latter being connected by a wire 134 to a cable 136 leading to the recording head for track A of the tape recorder unit.

The output circuit of the amplifier 14 comprises a wire 138 connected with the anode 44 and with a coupling capacitor 140 which is in turn joined to a resistor 142 connected by a wire 144 to the cable 136. The cathode 132 of the amplifier 14 is connected to a cathode resistor 146 which is grounded at 148; a bypass capacitor 150 bridges the cathode resistor 146. The input circuit of the amplifier 14 comprises a lead wire 152 which comes from the cable 18 and is connected through resistors 154 and 156 -to the control grid 38 of the triode. A grid rresistor 158 connects between ground and the junction of the resistors 154, 156.

In accordance with the invention there is provided a novel remote control for the oscillator 10, which is in addition to the proximal control comprising the switches 88, 96. Such remote control involves very simple circuitry in the form of a single control wire 160 and the signal cable 18 and which terminate at a control switch 162 located at the remote point 20. The switch 162 may have one terminal grounded, as shown.

At the recording unit 16 the cathode 28 of the oscillator 10 is connected to the load circuit of the oscillator by a current-modifying means in the form of a cathode resistor 164 which is grounded at 166. A bypass capacitor 168 bridges the resistor 164, and the cathode 28 is additionally connected to the control wire whereby its potential may be brought to ground potential whenever the remote control switch 162 is closed. Such closing of the switch 162 short circuits the cathode resistor 164 to alter the potential on the cathode 28 in such a manner as to render the oscillator 10 operative, whereas the oscillator is normally inoperative when the cathode resistor 164 is included in the cathode or load circuit without being bypassed or shoited by the switch 162. The terminals of the resistor 164 are hereinafter referred to as two different points of the energizing circuit, to which the wires 18a and 18h are connected, whereby the switch 162 can short circuit the resistor.

Thus, by the above organization either the remote control 162 or the proximal control 88, 96 may at all times function in the nature of a master, for effecting an inoperative condition of the oscillator 10, since each may dominate the other for this purpose. Further, -both controls 162 and 88, 96 must be set in their operative positions for the oscillator 10 to be conditioned for recording purposes utilizing track A of the tape recorder unit. The proximal control 88, 96 provides for the application of B`l voltage to the oscillator 10 and input amplifier 14. When such voltage is applied and when the remote control switch 162 is closed, recording on track A may be effected by the application of an input signal to the terminal 170 at the remote location 20. When this signal is terminated, the operator at the remote point (as for example, the instructor) may reopen the switch 162 whereupon the amplifier 14 and the oscillator 10 will be rendered inoperative.

With the present unit, the student may record at any time on track B, utilizing the microphone 74, the only requirement being that the control switch 88, 96 be in either of the two operative (or on) positions. For only one of such on positions the instructor at the remote point 20 may at any time record on track A by merely closing the remote control switch 162. Thus, when the recorder unit 16 is in use by the student it is necessary for him to effect the proper placement of the switch 8S, 96 to enable the instructor to record a signal applied to the terminal 170 on track A of the tape recording unit. Activating of the oscillator 10 and amplifitr 14 to effect such recording may only 4be done by the student at the unit 16 as regards the energization of these with Bt-lvoltage whereby they are conditioned and placed in readiness for whatever action is desired by the instructor at the remote point 20.

The frequency of oscillation of the oscillator 10 is determined by the circuit constants; also, such oscillator may be driven by a signal derived from the master oscillator 12, fin the following manner: a wire 172 may lead from the cathode 30 of the master oscillator to a coupling capacitor 174 which is in turn connected by a wire 176 to the control grid 34 of the oscillator 10. A grid resistor 178 connects between the wire 176 and the ground 166.

The organization as above set forth is seen to -be relatively simple, and to involve few components in a simple and straight-forward circuitry. Further, the control from the remote point by which the input amplifier and oscillator are rendered operative involves the single control wire 160 and the simple grounding switch 162, this control means being at most at relatively low potential not greatly different from ground potential. Accidental grounding or shorting of the control wire 160 and switch 162 accordingly can cause no damage to the equipment, but will merely mean that the oscillator 10 and the amplifier 14 will lbe placed in operative or recording condition. Thus, there is involved a safety feature, in addition to the simplification, by virtue of the single, groundingtype remote control organization.

Variations and modiiications may be made Within the scope of the claims, and portions of the improvement may be used Without others.

I claim:

1. In a student instruction station of an audio teaching apparatus, a recording unit comprising, in combination:

(a) a iirst electronic oscillator,

(b) said oscillator having an energizing circuit,

(c) a control switch means located at said oscillator and adapted for operation by the student, said switch means being connected in series in the said energizing circuit to control energization of said oscillator,

(d) a control cable having two wires respectively connected to two different points of said circuit,

(e) a switch disposed at a location remote from said oscillator and connected to said two wires,

(f) a current-modifying means at the oscillator connected to said two dierent points to be in series in said energizing circuit, for conditioning the oscillator to be inoperative, said switch at the remote point `being capable of effecting a short circuit of said current-modifying means so as to place the oscillator either in operating condition or else in non-operating condition while the same is connected for energization by said control switch means.

2. A device as in claim 1, wherein:

(a) the oscillator comprises a valve device having a plurality of cooperative elements one of which is connected to said circuit and is at ground potential when the switch renders the oscillator operative,

(b) one wire of said control cable being connected to said one element and the other wire being grounded to eiiect a grounding of the element for placing the oscillator in operative condition.

3. A device as in claim 2, wherein:

(a) the valve device comprises a vacuum tube,

(b) said one element of the valve device comprising the cathode thereof.

4. A device as in claim 1, characterized by:

(a) a second and continuously-operating master oscillator, and

(b) means coupling said irst oscillator to the second oscillator to lbe driven thereby.

S. A device as in claim 4, wherein:

(a) there is a signal amplifier having an output circuit coupled to the output circuit of the first oscillator, for recording signals,

(b) said signal amplifier having an energizing circuit connected to the energizing circuit of the lirst oscillator to obtain simultaneous energization of the oscillator and amplifier by operation of the said control switch means, and

(c) an input circuit connected with said amplifier, to

enable signals to be impressed thereon.

6. A device as in claim 4, wherein:

(a) the master oscillator has an energizing circuit connected with the said control switch means to be energized simultaneously with energization of the said first ocsillator.

7. A device as in claim 4, wherein:

(a) the said control switch means has an additional circuit to eiiect energization of the master oscillator apart from energization of the first oscillator,

(b) said master oscillator having an output circuit, and

(c) a signal input circuit and an input cable connected with the input circuit and leading from the oscillator to a remote point, said signal input circuit being coupled to the master oscillator output circuit to mix a signal and the oscillator output for recording.

References Cited by the Examiner UNITED STATES PATENTS BERNARD KONICK, Primary Examiner.

TERRELL W. FEARS, Assistant Examiner. 

1. IN A STUDENT INSTRUCTION STATION OF AN AUDIO TEACHING APPARATUS, A RECORDING UNIT COMPRISING, IN COMBINATION: (A) A FIRST ELECTRONIC OSCILLATOR, (B) SAID OSCILLATOR HAVING AN ENERGIZING CIRCUIT, (C) A CONTROL SWITCH MEANS LOCATED AT SAID OSCILLATOR AND ADAPTED FOR OPERATION BY THE STUDENT, SAID SWITCH MEANS BEING CONNECTED IN SERIES IN THE SAID ENERGIZING CIRCUIT TO CONTROL ENERGIZATION OF SAID OSCILLATOR, (D) A CONTROL CABLE HAVING TWO WIRES RESPECTIVELY CONNECTED TO TWO DIFFERENT POINTS OF SAID CIRCUIT, (E) A SWITCH DISPOSED AT A LOCATION REMOTE FROM SAID OSCILLATOR AND CONNECTED TO SAID TWO WIRES, (F) A CURRENT-MODIFYING MEANS AT THE OSCILLATOR CONNECTED TO SAID TWO DIFFERENT POINTS TO BE IN SERIES IN SAID ENERGIZING CIRCUIT, FOR CONDITIONING THE OSCILLATOR TO BE INOPERATIVE, SAID SWITCH AT THE REMOTE POINT BEING CAPABLE OF EFFECTING A SHORT CIRCUIT OF SAID CURRENT-MODIFYING MEANS SO AS TO PLACE THE OSCILLATOR EITHER IN OPERATING CONDITION OR ELSE IN NON-OPERATING CONDITION WHILE THE SAME IS CONNECTED FOR ENERGIZATION BY SAID CONTROL SWITCH MEANS. 